P0120
Fix within a few daysThe engine computer detects an incorrect voltage signal from the primary Throttle Position Sensor (TPS). This sensor tells the computer how much the throttle plate is open.
Code P0120 means your engine computer detects an issue with the Throttle Position Sensor. Common causes: Faulty TPS (70%), wiring issues (25%). Drivability: Yes, but with caution. Repair cost: $30-$150 DIY, $100-$300 professional.
Can I Drive With P0120?
Limit driving, fix within a few days
Essential trips under 10 miles, avoid highways and heavy traffic due to potential stalling or unpredictable acceleration.
Stop driving immediately if: Frequent stalling, severe power loss, or uncontrolled acceleration.
Symptoms of P0120
- 1Engine hesitation or surging during acceleration
- 2Rough or erratic idle
- 3Engine stalling, especially when coming to a stop
- 4Poor or inconsistent acceleration
- 5Check Engine Light illuminated
Common Causes of P0120
Parts most likely causing this code, ranked by probability
A faulty TPS sends incorrect voltage signals to the engine computer, causing it to misinterpret throttle plate position.
70% of P0120 cases are fixed by replacing the Throttle Position Sensor
Damaged, corroded, or loose wiring and connectors to the TPS can interrupt or distort the sensor's signal.
25% of P0120 cases are fixed by repairing wiring or connectors
A rare internal fault within the engine computer can incorrectly process the TPS signal or fail to provide proper reference voltage.
5% of P0120 cases are fixed by replacing the Engine Control Module
Check These First (Before Buying Parts)
- Visually inspect the Throttle Position Sensor (TPS) and its electrical connector for any visible damage, corrosion, or loose wires.
- Ensure the throttle body itself is not excessively dirty or sticking, which can mimic TPS issues.
How to Diagnose P0120
- 1Visually inspect the Throttle Position Sensor (TPS) and its wiring harness for any obvious damage, corrosion, or loose connections.
- 2Using a multimeter, test the voltage output of the TPS at various throttle positions (key on, engine off) to ensure it sweeps smoothly from low to high voltage without drops or spikes.
- 3Check for proper reference voltage (typically 5V) and ground at the TPS connector.
- 4If available, use a scan tool to monitor live data for the TPS voltage while slowly opening and closing the throttle plate; look for smooth, consistent readings.
- 5If all sensor and wiring checks pass, consider further diagnosis of the Engine Control Module (ECM/PCM) by a professional.
P0120 on Popular Vehicles
Toyota Camry
2002-2006TPS failures are common, sometimes requiring replacement of the entire throttle body if the sensor is integrated.
65% fixed by TPS replacement
Honda Accord
2003-2007Similar to Camry, TPS issues can be prevalent, often leading to rough idle and hesitation. The TPS might be a separate component or part of the throttle body.
60% fixed by TPS replacement
Ford F-150
2004-2008P0120 is frequently seen on these trucks, causing symptoms like erratic idle, stalling, and poor acceleration. The TPS is typically a replaceable sensor on the throttle body.
75% fixed by TPS replacement
Frequently Asked Questions
What does P0120 mean?
P0120 indicates that your vehicle's engine computer has detected an electrical malfunction in the primary Throttle Position Sensor (TPS) circuit. This sensor tells the computer how much the throttle is open.
Can I drive with P0120?
Yes, you can drive with P0120, but with caution. The engine might hesitate, stall, or accelerate unpredictably, making it unsafe for long trips or heavy traffic. Fix this within a few days to prevent unsafe driving conditions.
Will P0120 clear itself?
No, P0120 will not clear itself. The underlying electrical fault or sensor malfunction requires diagnosis and repair. The Check Engine Light will remain on until the issue is resolved and the code is cleared, or the vehicle completes several drive cycles without the fault.
How do I fix P0120 myself?
Start by visually inspecting the TPS wiring and connector for damage. If they look good, test the TPS voltage with a multimeter. If the sensor output is erratic or incorrect, replace the Throttle Position Sensor. This often involves removing a few bolts and disconnecting a wiring harness.
How much does it cost to fix P0120?
DIY repair for P0120 typically costs $30-$150 for a new Throttle Position Sensor. Professional repair at a shop usually ranges from $100-$300, including parts and 1-2 hours of labor.
P0120 keeps coming back - why?
If P0120 keeps returning, it indicates the initial repair did not address the root cause. This often means the wiring harness to the TPS has an intermittent fault, the connector is still bad, or in rare cases, the Engine Control Module (ECM) itself is faulty. Double-check all connections and wiring thoroughly.
Will P0120 fail emissions/smog test?
Yes, P0120 will cause your vehicle to fail an emissions or smog test. An active Check Engine Light, especially for a sensor critical to engine operation like the TPS, is an automatic failure in states with such inspections.
What's the difference between P0120 and P0121?
P0120 indicates a general electrical circuit malfunction with the Throttle Position Sensor 'A'. P0121 specifically means the TPS 'A' circuit range/performance is out of expected limits, suggesting the sensor is working but providing implausible readings, rather than a complete circuit fault.
P0120 on Ford F-150
On many Ford F-150 models, especially 2004-2008, P0120 is a common code often caused by a failing Throttle Position Sensor. Symptoms include erratic idle, stalling, and poor throttle response. Replacing the TPS is a direct fix for most cases.
Questions to Ask Your Mechanic
Did you test the TPS voltage output with a multimeter across its full range of motion?
Good answer: Yes, I checked the voltage sweep from closed to wide-open throttle, and it had flat spots or erratic readings, indicating a bad sensor.
What were the reference voltage and ground readings at the TPS connector?
Good answer: I confirmed a steady 5V reference and a solid ground at the connector, which means the wiring to the sensor is good.
Repair Cost Estimate
DIY Repair
Parts only
$30-$150
Shop Repair
Parts + labor
$100-$300
Save $70-$150 by doing it yourself
Difficulty
intermediate
Time
0.5-1.5 hours
Intermediate - requires basic hand tools and a multimeter for accurate diagnosis. A scan tool for live data is a plus.
Cost of Waiting
Ignoring P0120 leads to unreliable engine performance, including stalling and unpredictable acceleration. This creates unsafe driving conditions and can leave you stranded. A $50 sensor replacement now prevents a potential tow bill and dangerous driving situations.
While You're In There...
Cleaning the throttle body while accessing the TPS can improve idle quality and throttle response, preventing future issues related to carbon buildup.
If you remove the entire throttle body to access the TPS or clean it thoroughly, replacing the gasket prevents vacuum leaks.
Tools You'll Need
- Basic hand tools (sockets, wrenches)
- Multimeter
- Scan tool (optional, but helpful for live data)
P0120 is a common sensor code that directly affects how your engine responds to the gas pedal. Most repairs involve replacing an inexpensive sensor, and your vehicle's drivability will be restored afterward.
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Your Next Steps
Step 1: Perform a thorough visual inspection of the TPS wiring harness and connector for any signs of damage, fraying, or corrosion. Ensure the connector is securely seated.
Step 2: If the visual inspection is clear, use a multimeter to test the TPS. With the key on and engine off, backprobe the TPS connector to measure the voltage output as you slowly open and close the throttle by hand. Look for a smooth, consistent voltage sweep without any sudden drops or spikes.
Step 3: If the TPS voltage is erratic or incorrect, replace the Throttle Position Sensor. If the sensor tests good, investigate the wiring for continuity and check the ECM for proper reference voltage and ground.